Yeah, I use gaming mode for my TV-as-a-monitor and if I don't the lag is noticeable even on the desktop. It has the nice side effect of disabling the obnoxious sharpening filters, too.

My dedicated monitors have had dismal reliability: one died right after the warranty, one died inside the warranty and they flaked on the warranty anyway. My reliability expectations are rock bottom, my TV will have to work hard to undershoot them.